This invention relates to metal casting apparatus and more particularly to such apparatus for casting measured quantities of molten steel.
It is well-established practice to provide metal casting apparatus including a container, such as a ladle, a tundish or a casting box, provided with an outlet nozzle in the base of the container, flow of molten metal from the container through the nozzle to an associated mould being under the control of an elongate stopper located vertically within the container and having a lower hose end co-operating with the nozzle whereby axial movement of the stopper relative to the container opens and closes the nozzle in accordance with the desired flow rate of the molten steel.
Prior to casting, the container and associated equipment are pre-heated, typically to a temperature of the order of 1000.degree. C., to reduce the thermal shock of the refractory material when the container is filled with molten metal from the furnace, this molten metal being at a temperature of up to 1600.degree. C.
The container is then positioned over a mould to be poured with the stopper seating in the nozzle to close the nozzle. The stopper is raised in a controlled manner to allow molten metal to flow into the mould, and, when the mould is full, the stopper is lowered to stop said flow of metal.
The container or mould is then moved on to allow the next mould to be poured and this sequence is continued until the container is empty of molten metal, the stopper then being lowered down to close the nozzle and locked in this position.
During the casting process, slag is formed within the container. The slag is lighter than the molten metal and therefore accumulates on the surface of the molten metal. Thus, once the container is emptied of molten metal, a quantity of slag remains therein around the lower end of the stopper and the nozzle.
Prior to refilling the container with a fresh supply of molten metal, it is necessary to remove the slag from the container and this is achieved by inverting the container whereby the slag can fall or be raked from the container.
However, the relatively fragile construction of the stopper support mechanism, and in particular the so-called rotor rod by which the stopper is conventionally attached to the transverse support arm, can result in damage to, or breakage of, the stopper during such inversion and therefore require replacement of the stopper at significant cost.
U.S. Pat. No. 450824 details a more rigid stopper support mechanism less prone to damage during inversion than the aforementioned conventional arrangements incorporating rotor rods.
After removal of the slag, the container and associated equipment are repositioned in their upright positions, preheated and refilled with molten metal for subsequent casting processes. The above-described procedure is then repeated.
However, serious problems can arise which adversely affect the working life of the component parts of the equipment, in particular the stopper.
The inevitable formation of slag and the collection of this slag around the nose end of the stopper together with the wear of the stopper, in particular the nose end thereof, that inevitably occurs during the casting process, combine to cause the nose end of the stopper to adhere to the nozzle. Thus, on subsequent raising of the stopper to open the nozzle, the adhesion of the stopper to the nozzle must first of all be overcome and this can and does result in breakage of the stopper such that a replacement stopper must be installed. Furthermore, even if the adhesion is overcome, there is often damage to the nose end of the stopper that can result in leakage paths from the container through the nozzle even with the stopper in the lowered position seating in the nozzle.
Thus it will be appreciated that the number of container fills for which a given stopper can be used is very variable and at the worst could be such as to require a separate stopper for each cast. Clearly this is financially and commercially unacceptable.